This invention relates to integrated circuits such as programmable logic device integrated circuits, and more particularly, to hotsocket circuitry for programmable logic devices and other integrated circuits.
Integrated circuits such as programmable logic devices have power pins and data pins. The power pins on an integrated circuit chip are used to supply power supply voltages to internal circuitry on the chip. The data pins are coupled to input-output (I/O) circuits that are typically located around the periphery of the chip. Data pins are used to convey data signals to and from the I/O circuits.
The pins on an integrated circuit are often used to form communications ports. Commonly-used ports include ports that support standards such as the universal serial bus (USB) standard, the Firewire standard (IEEE 1394), etc. Electronic components that use these ports are often designed to be hot swappable. A hot-swappable component can be inserted into a system or removed from a system without powering down the system.
When a hot-swappable peripheral is connected to a powered port, it is not known in advance which pins in the port will be the first to make electrical contact with each other. If a user inserts a peripheral in one way, the power pins in the port may be the first to be electrically connected with each other. If, however, the user inserts the peripheral in a slightly different way, the data pins may be the first to make electrical contact with each other. This type of uncertainty about the order in which the data and power pins are connected must be taken into account when designing integrated circuits for hot swappable applications. For example, such circuits should be designed to avoid circuit failures in situations in which the data pins of the integrated circuit receive signals before the power supply pins have received power and before the circuits of the integrated circuit have had an opportunity to be properly powered up and establish normal operating conditions.
To provide tolerance to hot swapping, integrated circuits such as programmable logic devices have employed so-called hotsocket detectors to detect when the data pins receive signals before the power pins. This type of out-of-order scenario is often referred to as a hotsocket condition.
It would be desirable to be able to provide improved hotsocket detector circuitry on integrated circuits such as programmable logic devices.